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Nocardia seriolae, a gram‐positive branching filamentous bacterium, is the causative agent of fish nocardiosis. It mainly infects fish through gills, anus, lateral line or surface injury, resulting in a large number of white nodules in visceral organs and skin ulcerations. N. seriolae can infect about 42 species of fish and severely harm the aquaculture industry in many regions, particularly in Asia. Aiming to have a more comprehensive understanding about N. seriolae, the literature of N. seriolae before January 2022 was collected by searching nine databases and the current knowledge of the host diversity, drug resistance, genotype and phenotype, virulence factor, molecular detection and vaccine development of N. seriolae was summarized in this review. The future studies of N. seriolae are also prospected in order to help the research on the pathogenic mechanism and control of N. seriolae infection. [ABSTRACT FROM AUTHOR]

Nocardia seriolae has been identified as the causative agent of fish nocardiosis, resulting in serious economic losses in aquaculture. With an aim to screen potential candidates for vaccine development against N. seriolae , the in vivo -induced genes of N. seriolae in hybrid snakehead (Channa maculate ♀ × Channa argus ♂) model were profiled via in vivo -induced antigen technology (IVIAT) in the present study, and 6 in vivo -induced genes were identified as follows: IS701 family transposase (is701), membrane protein insertase YidC (yidC), ergothioneine biosynthesis glutamate-cysteine ligase (egtA), molybdopterin respectively-dependent oxidoreductase (mol), phosphoketolase family protein (Ppl), hypothetical protein 6747 (hp6747). Additionally, the yidC was inserted into eukaryotic expression vector pcDNA3.1-myc-his-A to construct a DNA vaccine named as pcDNA-YidC to evaluate immunoprotection in hybrid snakehead after artificial challenge with N. serioale. Results showed that the transcription of yidC was detected in spleen, trunk kidney, muscle and liver in vaccinated fish, suggesting that this antigenic gene can be recombinantly expressed in fish. Meanwhile, indexes of humoral immunity were evaluated in the vaccinated fish through assessing specific-antibody IgM and serum enzyme activities, including lysozyme (LZM), superoxide dismutase (SOD), acid phosphatase (ACP) and alkaline phosphatase (AKP). Quantitative real-time PCR analysis indicated that pcDNA-YidC DNA vaccine could notably enhance the expression of immune-related genes (CD4 、 CD8α 、 MHCIIα 、 TNFα 、 IL-1β and MHCIα) in 4 tissues (spleen, trunk kidney, muscle and liver) of the vaccinated fish. Finally, an immuno-protection with a relative survival rate of 65.71 % was displayed in vaccinated fish in comparison to the control groups. Taken together, these results indicate that pcDNA-YidC DNA vaccine could boost strong immune responses in hybrid snakehead and show preferably protective efficacy against N. seriolae , indicating that IVIAT is a helpful strategy to screen the highly immunogenic antigens for vaccine development against fish nocardiosis. • Six antigenic genes of Nocardia seriolae were screened via IVIAT technology. • The pcDNA-yidC was constructed and used as DNA vaccine to induce immune responses. • The trials of pcDNA-yidC DNA vaccine could provide 65.71 % RPS. • IVIAT can be used as a strategy to study the antigenic genes for vaccine development against N. seriolae. [ABSTRACT FROM AUTHOR]

Glutamic endopeptidases (Glu), belonging to the class of serine proteases, are a subfamily of chymotrypsin‐like proteolytic enzymes, which are regarded as important virulence factors in bacteria. However, the roles of glutamic endopeptidases of Nocardia seriolae in pathogenic process still remain uncertain. Here, a glutamic endopeptidase homolog from N. seriolae (GluNS) was cloned and its function was elucidated. GluNS encoded a 414‐aa protein which shared 93% identity to N. concava. In the phylogenetic tree, the glutamic endopeptidases of genus Nocardia clustered together firstly and then clustered with Streptomyces species. Moreover, GluNS was identified to be a secreted protein of N. seriolae and localized in the mitochondria of FHM cells. The transient overexpression of GluNS significantly induced increase in caspase‐3 activity and decrease in ΔΨm values in FHM cells. The number of apoptotic bodies was remarkably higher than that in control group. Taken together, GluNS overexpression induced apoptotic characteristics in FHM cells. This study provided new insights into the function of glutamic endopeptidase from N. seriolae. [ABSTRACT FROM AUTHOR]

Nocardia seriolae, a Gram‐positive bacterium, is the main pathogen of fish nocardiosis. Protein NlpC/P60 is a cell‐wall peptidase and a potential virulence factor of N. seriolae. Subcellular localization research revealed that both NlpC/P60‐GFP and NlpC/P60Δsig‐GFP fusion proteins were evenly distributed in the whole cell of fathead minnow (FHM) cells. Furthermore, typical apoptotic features, such as nuclear pyrosis and apoptotic bodies, were observed in the transfected FHM cells and grouper spleen cells by the overexpression of protein NlpC/P60. Then, quantitative assays of mitochondrial membrane potential (ΔΨm) value, caspase‐3 activity and apoptosis‐related gene (Bax, BNIP3, TNF1 and TNF6) mRNA expression were conducted. The results showed that ΔΨm was decreased, caspase‐3 was significantly activated, and the mRNA expression of pro‐apoptotic genes (Bax and BNIP3) and tumour necrosis factors (TNF1 and TNF6) was up‐regulated in NlpC/P60‐overexpressed cells. Taken together, the results indicated that the protein NlpC/P60 of N. seriolae might involve in apoptosis regulation. This study may lay the foundation for further study on the function of N. seriolae NlpC/P60 and promote the understanding of the virulence factors and pathogenic mechanism of N. seriolae. [ABSTRACT FROM AUTHOR]

Fish nocardiosis is a widespread chronic granulomatous disease in aquatic environment, which was particularly caused by Nocardia seriolae. The phage shock protein A (PspA) and tellurium resistance protein D (TerD) were identified to be the immunodominant antigens of the wild-type N. seriolae strain ZJ0503 in our previous study. In an attempt to develop effective DNA vaccines against this pathogen, PspA and TerD were used as candidates to ligate with pcDNA3.1-Flag plasmids, respectively. In addition, the abilities of these two DNA vaccines to elicit various immune responses in hybrid snakehead and supply protective efficacy against artificial challenge with N. seriolae were determined in the present study. The results showed that intramuscular injection with pcDNA-PspA and pcDNA-TerD did not exhibit cytotoxic activities in hybrid snakehead via histopathological examination. Besides, hybrid snakehead immunization with pcDNA-PspA and pcDNA-TerD could increase several non-specific immune paraments in serum, including LYZ, POD, ACP, AKP and SOD activities. Meanwhile, the pcDNA-TerD DNA vaccine could induce strongly specific antibody (IgM) titer in hybrid snakehead with a relative percent of survival (RPS) value of 83.14% against N. seriolae , while that of pcDNA-PspA DNA vaccine was displayed comparably low IgM titer with RPS value of 57.83%. Furthermore, quantitative real-time PCR assays presented that the expression of immune-related genes (MHCIα , MHCIIα , CD4 , CD8α , IL-1β and TNFα) were up-regulated to various degrees after vaccination with pcDNA-PspA or pcDNA-TerD, indicating that these two DNA vaccines were able to boost humoral and cell-mediated immune responses in hybrid snakehead. Taken together, both the pcDNA-PspA and pcDNA-TerD DNA vaccines were proved to be safe, immunogenic and effective in protecting hybrid snakehead against N. seriolae infection, which can promote the development and application of DNA vaccines to control fish nocardiosis in aquaculture. • Two DNA vaccines were prepared by utilizing the ribosomal proteins (PspA and TerD) as antigens for treatment of fish nocardiosis. • Both DNA vaccines not only did not exhibit cytotoxic activities but also could boost the innate, humoral and cellular immune response in hybrid snakehead. • Two DNA vaccines show highly protective efficacy against N. seriolae infection in hybrid snakehead with relative percentage survival (RPS) of 57.83% and 83.14%, respectively. [ABSTRACT FROM AUTHOR]